Metal buildings and lightening sort of OT

Excuse the lengthy OT message, but I noticed that folks in this group have built metal buildings for their workshops and though you might be able to help me.

I am considering building a large garage/pole barn using metal.

I am very concerned with lightening strikes due to where I live.

My house is nearly the highest thing in town. When we get lightening it's always dancing around us. There had been a tree next to the house about 30 years ago, it would get hit by lightening and they finally put a lightening rod in it. Eventually got taken out anyway (big tree they cemented back together at one point). It was gone when I got here, but I had to deal with the stump which is when I found the braided wire from the lightening rod.

The roofs of the additions that were put on in the 20's were all metal covered with tar. It's clear they were not maintained, as many interior walls had damage, so they were probably exposed as I found them for some time. The chimneys on either end of the house had lightening rods, each fastened to their own ground, not in the middle which I think would have been the right thing to do. The ligtening rods were disconnected for at least the last 13 years (since we've been here), but I just had to spend 3 grand having the tops of both rebuilt as they were loose from being hit by lightening, and bricks had started falling down.

We have an old three holer outhouse that is now a garden shed. It had the same sheet metal roof in hip form, and I liked the look so left it alone (unlike the house where I had the metal torn off and replaced with a membrane roof). One day I was mowing the lawn and found a piece of rusty metal, I looked over at the back of the outhouse and there was a big burn mark and at least 3 feet of the roof had been blown off.

When I was making some changes to a small old hay barn so my wife could use the second floor, I noticed what looked like some singed paper on the roof. Further inspection showed that it had also had a metal roof, and had clearly been hit and burned by lightening.

If I look off into the woods on the hill to the left of our house, I can see trees that used to be green that got whacked by lightening and died from the hits (we think we know when it happened, helluva a storm, but of course it took years for everything to go bare).

When we walk in the woods behind our house, every now and then we find a tree top and occassionaly a whole tree that was clearly struck by lightening.

I've searched around the net and can't seem to find any real input on this. Someone told me that if I properly bond the building, I'll be all set. Well this makes sense except it makes me wonder if a 30x60 chunk of metal is going to be so attractive that it will invite the lightening and I'll end up with strikes on my wooden buildings?

Any real world experience would be greatly appreciated, since everything I have found on lightening seems inconclusive.

Sorry for the lengthy post, and thanks for any feedback. If emailing, remove nospam.

Reply to
nospamgoingjag
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A metal building is probably the best thing to be in, actually. It forms what is known as a "faraday cage", and allows the lightning to find a clear path to ground that doesn't involve going through you. Ground it well, and you should be fine.

No, it'll attract the lightning to itself. You want it to be the most attractive to the lightning, so ground it well and give the lightning some nice exciting pointy spikes to go for (serious).

Snodgrass lighning rods used to have a very informative site, maybe they're a place you could look.

Dave Hinz

Reply to
Dave Hinz

snip

Good thing it's no longer in active use!

Reply to
ATP*

Do a google search One example is

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I lived on the lower part of a hill that was regularly hit by lightning. The main power line that supplied the community came over that hill and every few years it got struck. If you have strikes so close it would be prudent to put up lighting rods. I have seen a hilltop above me being stuck by lightning while I was still securing my sailboat. There must have been a four inch spark that jumped between my fingers and the metal mast. The massive current that had to be at least half a mile away had induced enough current to feel like a live spark plug. Induced or stray currents can cause havoc with anything electronic nearby. At least put up a rod at the highest point on your property to draw a strike. Randy

Reply to
Randy Zimmerman

Don't shortcut the grounding system. A good system includes lightning rods, heavy wire (#6?), and ground rods. One good grounding system is an underground circle of heavy wire going all around the building, bonded to the building and the lightning rods. I recall that this is what they would use in rocky areas where ground rods cannot be driven in very far. The large industrial building I was associated with had heavy copper wire surrounding the building, about 20 feet away, as part of the ground system, with that bonded to ground rods and the building frame.

Be sure to bond everything to everything, bond the metal frame of the building to the lightning rod and the ground system. Actually, for a metal building, you could probably forget the lightning rods, and just ground the frame. However, if you are in a lightning prone area, better to overdesign it some. I recall some sources recommending heavy wire running across the ridge of the roof and then down to ground rods at both ends of the ridge.

The web site below shows a lightning protection system, although I think they don't put enough emphasis on the grounding.

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The state farm site has a good description, but not that good a picture.

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You did not say where the water table is on your property. The drier is is, the harder it is to get a good ground, so the more ground rods and the longer ground rods you will need. 10 foot ground rods are a good choice, if the soil will allow them, I noticed a couple of sources recomending the 10 foot length. In a perfect world, you would measure the resistance of the grounding system, but that is not that easy to do. Probably better to just drive more ground rods. One 10 foot ground rod at each corner of the building, bonded to the metal building frame, sounds pretty good to me. If the water table is high, maybe two ground rods would be enough.

You should be able to find something in the national electric code that would help you come up with a simple but effective lightning protection system, but when I took a look the advice seemed kind of vague, which is what you reported.

Lightning is ultimately unpredictable, but if you do the basics right you should be protected against most lightning strikes.

Given the history of your property, it might be worth it to hire a lightning consultant to give you specific recommendations. I think that the work could be done by you if you know what to do.

Richard

nospamgo> Excuse the lengthy OT message, but I noticed that folks in this group

Reply to
Richard Ferguson

Point lightning rods are no longer recommended for lightning rods. The lightning research center in Socorro NM discovered that a flat, stubby rod installed in arrays around the perimeter of the roof actually repel the buildup of the ground charge that precedes a strike. I imagine they have a web site. Visiting their research center can get real exciting, so to speak, during a storm. It is located on top of a mountain and has a large glass dome for observation. They send up balloons on steel cables to attract strikes and record their characteristics. I can't recall the name of the laboratory at the moment. Bugs

Reply to
Bugs

I looked up the Socorro lightning research center. Check:

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a good article and some great pictures taken at the Langmuir lab. Bugs

Reply to
Bugs

Interesting. I'll check that out, thanks.

Reply to
Dave Hinz

Perhaps not. Might just be the perfect cure for constipation!

Reply to
DeepDiver

I believe there is a general misunderstanding about how lightning rods work. It's not clear whether the original poster understood or not, so I'll just chime in anyway.

A static charge builds up in the air during a lightning storm. It originates in the clouds, but induces an electric field through the atmosphere. When the voltage between two points (two clouds, cloud and ground, or cloud and building, animal, person, tree, etc.) builds up to the breakdown voltage of air (on the order of 10,000 volts per inch distance) then an arc or spark (lighning) jumps between the two.

To prevent such arcing, you want to dissipate the electric field in the vicinity of your building.

Now, what's not always understood is how an electric field induces an opposite field in an object. I.e., if the cloud is negatively charged (sorry - I don't recall which charge the cloud normally will have) then it will induce a positive charge in the building.

The critical thing is that this positive charge will not be uniform across the building. It will be greater on the roof, and will have the greatest charge density at abrupt corners. What a lighting rod is is a VERY abrupt corner.

When the thunderstorm passes into the area and starts inducing electric charge on buildings, the charge density at the tip of the lighning rod becomes so intense as to leak current. This, in turn, dissipates the field. Exactly what we want to accomplish. (Thank you, Benjamin Franklin!) At the voltages we're dealing with here, this would be true whether or not the lighning rod were grounded. But the current to (from?) the rod must travel through something, and if the reisitance of what it must travel through is great, its voltage will rise to that of the air, ending its effectiveness at dissipating the charge. Hence, the rod must be grounded sufficiently to conduct whatever current it must, or else it will end up attracting lightning.

Hope this helps.

Reply to
freemab

Would be interesting to put an amp meter (clamp on or coil) on the conductor from the rod to the ground.

i
Reply to
Ignoramus9970

For a very short time, anyway ;) Then again, you do have some pretty large electrical toys, don't you...

Reply to
Dave Hinz

Well, a clamp on ammeter is not put in series with the current, it clamps around the conductor. I doubt that it would burn. I do indeed have a pretty large military surplus clamp on ammeter, that I kept for myself.

i
Reply to
Ignoramus9970

Yes, but there will be a hella-big current induced into the ammeter during the initial spike of current, no? It'd be interesting to see the waveform - I suspect a _very_ fast initial rise and a slow decay, but I could be very wrong. That initial spike, even though lightning is a DC phenomenon, has a lot of change in a short amount of time, and may induce quite a bit of current into your meter.

Imagine my surprise ;)

Have you ever been to American Science and Surplus, by the way? Seems like the kind of place you would enjoy. There's one in Milwaukee, and I seem to recall one down in your area as well.

Dave Hinz

Reply to
Dave Hinz

On Thu, 31 Mar 2005 22:38:57 -0500, "ATP*" wrote something ......and in reply I say!:

Glad I didn't let _that_ one fly in the living room!

****************************************************************************************** Whenever you have to prove to yourself that you are not something, you probably are.

Nick White --- HEAD:Hertz Music

remove ns from my header address to reply via email

!!

Reply to
Old Nick

Halloween night, 1956. We decide to steal an outhouse and put it on the front lawn of the high-school. Sneak into the farmers back yard, about 10 of us, and three guys go around to the back. Farmer must have decided to move it within the last few days, and had not covered over the old hole yet. Two guys fell in. They walked about 3 miles back to town. We wouldn't even let them in the back of one of the pickup trucks!

Brian Laws>On Thu, 31 Mar 2005 22:38:57 -0500, "ATP*" wrote

Reply to
Brian Lawson

I would be cautious about putting a clamp on ampmeter around the lightning system conductor. When installing lightning systems one wants to avoid sharp bends at all costs. Just a 90 degree bend can cause enough inductance that the lightning jumps to a nearby object.

A clamp on ampmeter would also add some inductance to the lightning system conductor.

Dan

Reply to
dcaster

To set the time frame for this tale; remember when motor oil came in real cans? (metal content)

A bunch of high school girls were having a Halloween slumber party about a half mile south of here up a gravel road. A bunch of girls attracts a bunch of boys; at my house since I lived closest to the slumber party.

WE decide to scare the girls. We had a lot of old farm machinery at our place. Among this collection was the front axle from a horse drawn wagon. WE decide to tie empty oil cans to the wheel spokes with baling wire and make a screaming run around the farm house full of girls. WE decide to put a handful of gravel in each can for effect. WE decide to hitch ourselves to the tongue with wire around our waists.

We sneak up their drive before tying the cans to the wheels. Someone gives the signal (there is always a signal) and away we go around the house a few times, yelling and making teenage boy noises.

The girls all run out on the porch screaming. You would think they would run inside if they were frightened. Female logic.

We break the circle, head down the drive and hit the gravel road back to my house. We still making all the noise we can when Vaughn falls down. With all the noise, no one notices in the dark. He's tied to the tongue with wire. The wheels run over him a few times and the cans are banging him pretty good. Anyway, after this half mile run and dragging Vaughn half that, we're really worn out. We darned near killed him.

We peeled off what was left of his clothes, layed him in the bed of a pickup and washed him off with a hose. He was cussing quite a bit. Of course, it was October. WE decided we had better take him home to his Mama. That would at least stop the cussing. It took two weeks of healing before he could come back to school.

Reply to
Andy Asberry

I've seen worse Andy. My buddies and I were drinking beer behind one guy's house - we didn't realize that one of the guys had jack daniels in his bottles until it was too late. So the other two of us had to figure out how to walk him home (we had driver's licenses by then, but were too smart to go driving around in that state) and inform his parents about the state of their son.

We were escorting him up the hill towards his house trying to sort the problem out in our mind when a guy in a VW bug came over the hilltop on the sidewalk and mowed us down, didn't even slow down or stop.

The guy we were bringing home got knocked spang out of his sneakers (really did happen, they were down the road apiece with the coat I had lent him) and gave him a compound fracture of his femur. That's a pretty strong bone in a 17 year old, too.

He spent more than two weeks, and it wasn't at home, before he could go back to school. They caught the guy because we gave a pretty good description and he left a bunch of his car trim bits on the roadside after hitting a street sign.

I still remember getting up after the car went by - the other guy who was with me, had my glasses in his hands. I had his. Never *did* figure that one out. It's a slap miracle that teenagers survive to adulthood.

Jim

Reply to
jim rozen

BIG SNIP

Speaking of home to Mama.....Leonard wasn't the brightest guy. In fact, the whole family combined wouldn't add to an IQ of 101. When Leonard was in his mid-teens, he had the chore of feeding the horses and dunging out the stalls at the local dairy, very early in the morning. I don't think he had ever learned to tie a knot, as he too often managed to let one or more of the horses out into the alley, and they would wander into the streets around the dairy. The delivery guys, much annoyed and worried for the safety of the horses, would have to chase and catch them before they could get hitched up and away on their routes. Finally, Leonard was threatened with dire consequences if he allowed this to happen again. He didn't listen. Next time it occurred, after the drivers retrieved the horses, they pulled Leonard's pants down and painted his privates and backsides in the dairy colour scheme, red and green and black. Leonard was quite upset, and ran home to Mama, who promptly cleaned off the still tacky paint with some turpentine.

You could hear Leonard scream for miles.

But you know, he never let a horse get loose again.

Reply to
Brian Lawson

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